1. Field of the Invention
The invention relates to a novel UV-stable transdermal therapeutic system (TTS) which consists of a backing layer, of at least one active ingredient-containing matrix and optionally of a detachable sheet, and comprises a UV absorber, with at least one UV absorber-containing adhesive layer being provided between the backing layer and the active ingredient-containing matrix which is furthest away from the surface of the skin, and at least one separating layer which is impermeable to active ingredient and impermeable to the UV absorber being present between the adhesive layer containing the UV absorber and the active ingredient-containing matrix which is furthest away from the surface of the skin.
2. Description of the Related Art
Attempts are known to employ photosensitive active ingredients which absorb UV-A and UV-B rays and normally in suncreams as described by Briscart & Plaizier-Vercammen (Proc. 2nd World Meeting on Pharmaceutics, Biopharmaceutics and Pharmaceutical Technology, APGI/APV, 1998, 1231-1232).
It is additionally known to protect transdermal therapeutic systems provided with photosensitive active ingredients by means of visually noticeable aluminized or lacquered cover sheets as backing layer of the TTS. DE-A1-19912623 describes a method for protecting therapeutic preparations, systems or ingredients thereof, the intention being to achieve protection, specific in each case, against breakdown by harmful factors such as atmospheric oxygen, water and/or light. Photoprotective substances which absorb or reflect electromagnetic waves are used, employing absorbing or reflecting agents whose absorption or reflection spectrum covers the wavelength range responsible for the instability of the photosensitive material or its ingredients. Coloured plastic sheets are used inter alia as cover sheet in this case, shown by the example of the 1,4-dihydropyridine derivative lacidipine.
The colouring of highly flexible plastic sheets proves to be difficult and does not provide reliable protection from light owing to fissures which frequently occur in the coloured layer of the plastic sheet.
Furthermore, DE-C1-10053375 discloses transdermal therapeutic systems (TTS) which consist of an active ingredient-containing polymer matrix and a backing layer, with polymer matrix and backing layer being firmly connected and forming a laminate, and both the polymer matrix and the backing layer containing a colourless substance which absorbs in the UV region and which has no intrinsic pharmacological effect. This solution is disadvantageous                in that interaction of the colourless substance which absorbs in the UV region with the active ingredient in the polymer matrix in some cases results in an unwanted influence on the stability of the TTS,        in that the firm connection between polymer matrix and backing layer which is permeable to active ingredient may result in extensive unacceptable diffusion of active ingredient from the polymer matrix into the backing layer, principally in the case of backing layers composed of polypropylene, polyethylene or polyurethane, and may finally emerge or crystallize out on the upper side of the backing layer/cover sheet,        in that skin irritation may be caused through direct contact of the skin with the substances which absorb in the UV region and which are present in the backing layer/cover sheet.        
It is therefore an object of the invention to provide a pharmaceutical preparation which is provided with a photosensitive active ingredient and is to be administered transdermally, and which achieves high stability without the aforementioned disadvantages.